The use of portable electronic devices is increasing nowadays as downsizing and weight-lightening of electronic equipment are possible due to development of the high-tech electronic industry, and the need for a battery having high energy density as a power source of such portable electronic devices is increasing.
A battery is a device for converting chemical energy that is generated during an electrochemical oxidation reduction reaction of a chemical substance in the battery into electrical energy, and can be classified as a primary battery that needs to be discarded when energy inside the battery is used up and a secondary battery that is rechargeable several times.
The secondary battery has an advantage of being able to be used by being charged and discharged several times using reversible interconversion between chemical energy and electrical energy. Particularly, because a lithium secondary battery has advantages of being rechargeable, having energy density per unit weight that is three times or more higher compared to an existing lead storage battery, nickel-cadmium battery, nickel-hydride battery, nickel-zinc battery, and the like, and being quickly chargeable, the lithium secondary battery is used in various ways as a driving power source of a portable electronic device such as a video camera, a cellphone, and a laptop computer.
The lithium secondary battery is used by injecting an electrolyte solution into a battery cell that includes a positive electrode including a positive electrode active material capable of intercalating and deintercalating lithium ions and a negative electrode including a negative electrode active material capable of intercalating and deintercalating lithium ions.
Because the lithium secondary battery is operated at a high driving voltage, a non-aqueous organic solvent in which a lithium salt is dissolved is used instead of an aqueous electrolyte that has high reactivity with lithium. The organic solvent is preferably stable at high voltage, has high ion conductivity and a high dielectric constant, and has low viscosity.
For example, when a carbonate-based polar non-aqueous solvent is used in the lithium secondary battery, an irreversible reaction in which an excessive amount of charge is used occurs due to a side reaction between a negative electrode/a positive electrode and an electrolyte solution during initial charging. Due to the irreversible reaction, a passivation layer such as a solid electrolyte interface (SEI) (hereinafter referred to as an “SEI film”) is formed at a negative electrode surface, and a protective layer is formed at a positive electrode surface.
The SEI film and the protective layer prevent decomposition of an electrolyte solution during charging and discharging and serve as an ion tunnel. Consequently, a life of a lithium secondary battery can be improved as the SEI film and the protective layer have higher stability and lower resistance.
Thus, to improve battery performance, the need for an organic electrolyte solution capable of forming an SEI film and a protective layer which have excellent stability and low resistance is coming to the fore.